/*
 * Copyright (C) 2016 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package apksigner;

import java.nio.ByteBuffer;

/**
 * Hexadecimal encoding where each byte is represented by two hexadecimal digits.
 */
class HexEncoding {

  private static final char[] HEX_DIGITS = "0123456789abcdef".toCharArray();

  /**
   * Hidden constructor to prevent instantiation.
   */
  private HexEncoding() {
  }

  /**
   * Encodes the provided data as a hexadecimal string.
   */
  public static String encode(byte[] data, int offset, int length) {
    StringBuilder result = new StringBuilder(length * 2);
    for (int i = 0; i < length; i++) {
      byte b = data[offset + i];
      result.append(HEX_DIGITS[(b >>> 4) & 0x0f]);
      result.append(HEX_DIGITS[b & 0x0f]);
    }
    return result.toString();
  }

  /**
   * Encodes the provided data as a hexadecimal string.
   */
  public static String encode(byte[] data) {
    return encode(data, 0, data.length);
  }

  /**
   * Encodes the remaining bytes of the provided {@link ByteBuffer} as a hexadecimal string.
   */
  public static String encodeRemaining(ByteBuffer data) {
    return encode(data.array(), data.arrayOffset() + data.position(), data.remaining());
  }
}
